Filed Pursuant to Rule 424(b)(3)
                                                     Registration Nos. 333-86212
                                                                    333-86212-01

PROSPECTUS SUPPLEMENT NO. 16
----------------------------

                                  $175,000,000

                                GATX Corporation

                     7.5% Convertible Senior Notes due 2007
                     Fully and Unconditionally Guaranteed by
                           GATX Financial Corporation
                                       and

                             Shares of Common Stock
                  issuable upon conversion of the Senior Notes

     This prospectus supplement supplements the prospectus dated June 19, 2002
of GATX Corporation and GATX Financial Corporation, as supplemented by
prospectus supplement no. 1 dated June 26, 2002, prospectus supplement no. 2
dated July 3, 2002, prospectus supplement no. 3 dated July 23, 2002, prospectus
supplement no. 4 dated August 9, 2002, prospectus supplement no. 5 dated August
29, 2002, prospectus supplement no. 6 dated September 12, 2002, prospectus
supplement no. 7 dated September 24, 2002, prospectus supplement no. 8 dated
October 3, 2002, prospectus supplement no. 9 dated October 9, 2002, prospectus
supplement no. 10 dated October 18, 2002, prospectus supplement no. 11 dated
October 31, 2002, prospectus supplement no. 12 dated November 18, 2002,
prospectus supplement 13 dated December 16, 2002, prospectus supplement no. 14
dated January 2, 2003 and prospectus supplement number 15 dated March 25, 2003,
relating to the sale by certain holders of our 7.5% convertible senior notes due
2007 and the shares of our common stock issuable upon conversion of the notes.
You should read this prospectus supplement in conjunction with the prospectus as
supplemented to date. This prospectus supplement is qualified by reference to
the prospectus as so supplemented except to the extent that the information in
this prospectus supplement supersedes the information contained in the
prospectus as so supplemented. Capitalized terms used in this prospectus
supplement and not otherwise defined herein have the meanings specified in the
prospectus.

     The table of Selling Holders contained in the prospectus is hereby amended
to add the entity named below as a Selling Holder:


                                        Principal Amount of
                                        Notes Beneficially      Number of Shares
                                            Owned That           of Common Stock
       Name of Selling Holder               May be Sold         That May be Sold
       ----------------------               -----------         ----------------

XAVEX - Convertible Arbitrage 7 Fund          $150,000                4,400
   c/o TQA Investors, LLC


     Investing in the notes and our common stock involves risks. See "Risk
Factors" beginning on page 5 of the prospectus.

     Neither the Securities and Exchange Commission nor any state securities
commission has approved or disapproved of these securities or passed upon the
accuracy or adequacy of this prospectus. Any representation to the contrary is a
criminal offense.

             The date of this prospectus supplement is July 8, 2003.